1. Field of the Invention
The present invention relates to a card-type wireless communication device and a wireless communication system incorporating it, having wireless communication capability, using a frequency-hopping system based on spread-spectrum technology, and connected to an information terminal device such as a personal computer.
2. Description of the Prior Art
In general, in communication using spread-spectrum technology at a transmitter, a modulated signal from an input base-band signal such as an audio signal, after having been spectrum-spread with diffusion codes, is transmitted to a receiver in the form of high-frequency signal. At the same time, at the receiver, the spectrum-spread signal received from the transmitter is demodulated (back diffused) using the same diffusion codes as used by the transmitter.
Communication systems that utilize spread-spectrum technology include a direct-spread system and a frequency-hopping system. In the direct-spread system, narrow-band modulated waves are multiplied by diffusion codes and spread among given continuous frequency bands. On the other hand, in the frequency-hopping system, an example of which is a technology called Bluetooth, carrier frequencies transmitted to the receiver are changed in a random order and transmission signals are spread among given frequency bands.
FIG. 7 is a block circuit diagram showing a simplified configuration of the conventional card-type wireless communication device. A conventional card-type wireless communication device 50 as shown in FIG. 7 has a circuit configuration described hereinafter. An antenna 51 is connected to a receiver circuit 52 and a transmitter circuit 57.
The receiver circuit 52 comprises an amplifier 53, a mixer circuit 54, and a demodulation circuit 55. The antenna 51 is connected to a base-band signal processing circuit 61 via the amplifier 53, the mixer circuit 54, and the demodulation circuit 55. Furthermore, the transmitter circuit 57 comprises a modulation circuit 60, a mixer circuit 59, and an amplifier 58. The base-band signal processing circuit 61 is connected to the antenna 51 via the modulation circuit 60, the mixer circuit 59, and the amplifier 58. The mixer circuits 54 and 59 are connected to a local oscillator 56.
The base-band signal processing circuit 61 is connected to a connector 65 via an interface circuit 62. Moreover, a circuit control block 63 is connected to each of the receiver circuit 52, the transmitter circuit 57, and the base-band processing circuit 61. A power supply circuit 64 is connected to the connector 65 and each of the aforementioned circuits of the card-type wireless communication device 50.
Next, how the conventional card-type wireless communication device functions is described. A signal sent from a transmitter and received through the antenna 51 by a receiver, in the form of spread-spectrum signal (e.g. 2.4 GHz band), is amplified by the amplifier 53 and fed to the mixer circuit 54. The high-frequency signal thus received is demodulated into a base-band signal by the mixer circuit 54 and the demodulation circuit 55. Then, the restored base-band signal is fed into the base-band signal processing circuit 61 for necessary signal processing and fed to an information terminal device (not shown) such as a personal computer through the interface circuit 62 and the connector 65.
At the transmitter, an input data signal fed from an information terminal device (not shown) such as a personal computer through the connector 65 and the interface circuit 62 is fed into the base-band circuit 61 for prescribed signal processing in, diffused as spread-spectrum signals (e.g. 2.4 GHz band) by the modulation circuit 60 and the mixer circuit 59, amplified by the amplifier 58, and transmitted to the receiver through the antenna 51.
The circuit control block 63 controls each operation of the receiver circuit 52, the transmitter circuit 57, and the base-band signal processing circuit 61. The power supply circuit 64 receives power from the information terminal device (not shown) such as a personal computer via the connector 65 and delivers a supply voltage +B to each of the aforementioned internal circuits of the card-type wireless communication device 50.
The local oscillator 56 generates a frequency signal (e.g. 2.4 GHz) required for function of each of the mixer circuits 54 and 59.
In the above-mentioned conventional technology, no particular problems relating to power occur as long as the information terminal device (not shown) such as a personal computer is operated on commercial power supply, because power is supplied from the information terminal device such as a personal computer to the power supply circuit 64 of the card-type wireless communication device 50 through the connector 65.
However, when the information terminal device such as a personal computer is carried and used as mobile equipment, the information terminal device such as a personal computer operates on a battery included therein and the power supply circuit 64 of the card-type wireless communication device 50 receives power from the battery included in the information terminal device such as a personal computer via the connector 65. As a result, the information terminal device such as a personal computer can only be used for a shorter period of time as mobile use, because an increase in power consumed by the card-type wireless communication device 50 results in faster discharge of the battery included in the information terminal device such as a personal computer.